We were recently referred an 8-month-old girl with a strong clinical history of PCD (respiratory and nasal symptoms since birth, situs inversus, and serous otitis media). Using high-speed video microscopy we recorded abnormal and hyperfrequent ciliary function at 37°C on four separate occasions, despite normal ciliary ultrastructure consistent with atypical PCD.5,6 On two occasions the CBF and CBP were assessed at 37°C and room temperatures (measured at 21°C-24°C). CBF from at least six separate ciliated cell clusters measured at 37°C was hyperfrequent on both occasions (mean, 26.3 Hz [SD ±3.4]; 34.4 Hz [SD ±13.5]). However, when measured at room temperature, the CBF measurements were within normal range (11-18 Hz) (mean, 12.6 Hz [SD ±0.8]; 15.2 Hz [SD ±4.5]). CBP at 37°C was consistently abnormal, with interrupted, dyskinetic, hyperfrequent ciliary beating, and cilia lacked the normal range of motion (Video 1). Cilia were directly compared on the same epithelial edge at 37°C and room temperature, and, as described previously, profoundly abnormal ciliary movement at 37°C (Video 1) reverted to a more normally coordinated beat pattern with a greater range of movement at room temperature (Video 2), suggesting a PCD variant with temperature-dependent CBP. We conclude that cooling of cilia to allow diagnostic interrogation of ciliary function, in the absence of temperature controlled high-speed video microscopy equipment, may be inappropriate for the diagnostic screening of nasal epithelium for PCD.